This invention relates to an improvement in the process for producing ethyl acetate and more particularly to the optimal placement of recycle streams and the use of a membrane separation unit to remove water from the resultant product stream.
Methods for producing a product ester by the esterification of a lower carboxylic acid with an alcohol in the presence of an esterification catalyst are well known in the art, see for example U.S. Pat. No. 5,231,222 and British Patents 1,173,089 and 1,262,645.
Ethyl acetate is produced first, by reaction over a strong acid catalyst. Second, the resulting vapors are passed through a distillation zone, then cooled and condensed, and then distilled a second time to provide ethyl acetate with few impurities.
In conventional production processes, a portion of the produced product (with or without some impurities) is used as an azeotropic agent in the initial reaction vessel.
Esterification conventionally is performed at the base of a distillation column or in a separate reactor. In the typical reaction zone an alcohol containing from 2 to 5 carbon atoms is reacted with a carboxylic acid containing from 1 to 4 carbon atoms in the presence of an esterification catalyst. The product ester is recovered using phase separation from a product ester-water azeotrope, see for example, European Patent EP 0521 488 B1 issued to Union Carbide. This patent describes the typical preparation of higher esters than ethyl acetate, but the same process is basically used.
Although any esterification reaction produces a mole of water per mole of ester, the needs of the distillation which removes the ester from the reaction zone as an azeotrope with water vary according to what ester is being produced. In the case of ethyl acetate, there is too much water produced in the reaction to match the water-ester azeotrope. In the production of other esters, butyl acetate for example, too little water is produced in the reaction to match the azeotrope. Adjusting this water to ester ratio in the distillation is important for economical production of the ester.
The table below illustrates examples of the differences between the stoichiometric water produced and the azeotropic composition.
Ref: Advances in Chemistry Series, 116, Azeotropic Data III, ACS, Washington, D.C., 1973.
For those esters which produce more water than the azeotrope will remove, an azeotropic agent must be added. For those situations, the present invention applies.
Control of the amount of water in the process, and critical introduction of water into various stages of the production process for ethyl acetate are has been a constant issue. The present invention is directed to a method for controlling water in the production process to provide an optimized production process. Further the invention is directed to points at which water can be removed from the production process to debottleneck the process.
Additionally, the present invention is directed to a method for control of the amount of resulting acid from the final ethyl acetate product, wherein the amount of acid present in the final product is less than about 50 ppm acetic acid.
Disclosed is an improved process to produce ethyl acetate, which contains minor amounts of acetic acid, typically less than about 50 ppm. Additionally, a process is disclosed for producing ethyl acetate by using an additional step to remove a substantial amount of water from a condensed reaction stream and recycling portions of that dried stream back into the production process. Another portion of the dried stream is processed in a second distillation zone to produce an ethyl acetate product.
More particularly, an improved process for producing ethyl acetate is disclosed comprising contacting acetic acid and ethanol in a reaction zone in the presence of an acid catalyst, distilling the formed vapors and condensing to form an organic phase rich in ethyl acetate and an aqueous phase rich in water, separating the phases and further distilling each phase to obtain a final purified ethyl acetate product and a water stream low in organic components, the improvement comprising directing at least a portion of the organic phase from the first distillation to the reaction zone.
An alternate embodiment of the present invention involves directing at least a portion of the organic phase from the first distillation to a membrane separation unit which removes water, alcohol, or a combination of water and alcohol from the organic phase rich in ethyl acetate